Infinitives, gerunds, and participles are
closely related to verbs, so first recall what verbs are.

Verbs are
conjugated (they show tense or time) and, when joined with a subject,
form a clause.

example: The
lion hunted the antelope. Hunted
is the verb in an independent clause.

example: After
the female lion moved onto the plain, she hunted antelope.
Moved is the verb of the dependent clause and hunted the
verb in the independent clause.

Infinitives are nonconjugated forms of verbs.
The infinitive form of the verb hunt is 'to hunt'. Infinitives
are parts of phrases.

example: To
hunt antelope was the lion's main
desire. Here the infinitive phrase functions
as a noun and subject.

example: To
huntantelope, the lion
first hid in the tall grass. Here the
infinitive phrase functions as an adverb. Remember, adverbs indicate where,
when, why, or how.

example: The
best way to hunt antelope depends on the season.
Here the infinitive phrase functions as an adjective (to hunt antelope
modifies way).

Present Participles are formed by adding
ing to the base verb and act as adjectives or parts of verbs.

example: Hunting
antelope,
the lion fed herself and her cubs. The
present participial phrase Hunting antelope modifies lion and
is an adjective.

example: The
lions hunting on the plains did not reduce antelope numbers.
The present participial phrase hunting on the plains modifies lions
and is an adjective.

example: The
hunting lion focuses on her prey.
Hunting is a present participle functioning as an adjective.

example: Thelions will be hunting antelope.
Hunting is a present participle functioning as part of the main
verb will be hunting.

Gerunds are
similar to present participles in that
both end in ing. But gerunds are nouns.

example: Hunting
antelope can be difficult.
The gerund hunting is a noun. The gerund phrase Hunting antelope
is the subject of the sentence.

Like other nouns, gerunds can serve as subjects,
direct objects and objects of prepositional phrases. See gerunds.

Past Participles
usually are formed by adding ed to the verb base. The past participle
of hunt is hunted. Past participles function in three ways.

example: Hunted
by lions, the antelope scattered
into the trees. The past participle hunted
is part of a phrase that modifies antelope. It's an adjective.

example: The
hunted antelope scattered into
the trees. Here the past participle is
a one-word adjective.

example: The
lions have hunted antelope. The past participle hunted is
part of the main verb (have hunted).

example: The
antelope will be hunted. The past participle hunted can
be considered part of a passive verb or an
adjective (better to consider it part of the transitive passive verb will
be hunted so that you recognize the transitive active verb).

example: The
antelope that was hunted today was male. The
dependent clausethat was hunted
todaycan be simplified to the
past participlephrase
hunted today: The
antelope huntedtoday was male.